A few months ago, Microsoft invested $15 million in location data company Foursquare. Foursquare looked like a great data partner for Microsoft, but it wasn’t clear how the two companies would work together. Foursquare has raised $121 million to date.

Now we know why Microsoft decided to invest so heavily in Foursquare. According to The Verge, Microsoft will use Foursquare location data in Cortana, a Siri-like voice assistant for Windows Phones. Cortana will be part of a new software update for Windows Phones that will launch this spring.

While Foursquare didn't directly say Cortana drove Microsoft to invest, it says partnerships like this are why the two companies paired up.

"Microsoft will use Foursquare’s data to augment Microsoft’s contextually-aware experiences in several current and upcoming Microsoft products, including Windows Phone and Windows and will provide an even richer local search experience in Bing," a Foursquare spokesperson told Business Insider.